This invention relates to an electrostatic chuck for holding semiconductor substrates during processing with corrosive gases, the chuck having improved corrosion resistance.
In the semiconductor industry, electrostatic chucks use electrostatic attraction forces to hold substrates, such as silicon wafers during processing. Electrostatic chucks are described in more detail in for example, U.S. Pat. No. 4,184,188 to Briglia; U.S. Pat. No. 4,399,016 to Tokuda; and U.S. Pat. No. 4,384,918, to Abe.
A typical electrostatic chuck comprises a pedestal having an electrode thereon covered by an electrically insulative layer. A voltage source is provided for electrically biasing the electrode so that electric charge can accumulate in the electrode and in the insulator. The accumulated electric charge generates an electrostatic force F that attracts and holds the substrate against the insulative layer. The force F is given by: ##EQU1## where .epsilon. is the dielectric constant of the insulative layer, V is the applied voltage, t is the thickness of the insulative layer, and A is the area of the conductive pedestal that serves as the electrode. Thus, to obtain a strong electrostatic attractive force, it is desirable to have a thin insulative layer which has a high dielectric constant .epsilon..
Typically, polyimides and other organic polymers are used as the insulative layer because of their high voltage breakdown strength and their superior chemical resistance. Also, the ability of the polyamide to conform to the backside of the substrate allows for good heat transfer for cooling the substrate during processing. However, polyimides and other organic polymers corrode rapidly when exposed to corrosive gases such as oxygen, chlorine, and fluorine used in processing of the silicon wafers.
During such processing with corrosive gases, a top surface of the insulative layer is substantially covered by the silicon wafer and protected from corrosion. However, the thin, side surfaces of the insulative layer are exposed to the corrosive gases and quickly corrode. After a short operation cycle, the thin insulative layer can be sufficiently corroded to allow the flow of electrons therethrough, causing arcing and malfunctioning of the chuck.
Protective coatings have been applied to the insulative layer in an attempt to slow the corrosion. However, these coatings can be expensive to manufacture and are not effective against all types of corrosive gases. Thus, there is a need for an electrostatic chuck having an insulative layer which is not quickly corroded by corrosive gases, thereby increasing the useful life of the electrostatic chuck.